When a film cartridge is loaded into a camera, it is necessary to insure that the film cartridge is firmly located in a known position to insure proper camera operation. In addition, several operations may occur during the cartridge loading sequence that require camera features to engage film cartridge features. For example, in one camera system, a double exposure protection sensor or hook engages the film cartridge to insure only unexposed film cartridges are loaded into the camera (see e.g. U.S. Pat. No. 4,994,828).
Another operation which can occur during film cartridge loading is the engagement of a camera light lock drive mechanism with an active light lock (ALL) of the film cartridge. The ALL on the cartridge is movable by the drive mechanism between an open position, allowing photographic film to exit the cartridge, and a closed position sealing the cartridge in a light-tight manner. The ALL door of the film cartridge is normally held closed by a lock pawl on the film cartridge. When a film cartridge is loaded into a camera loading chamber or other equipment (e.g. photofinishing apparatus), the lock pawl must be disengaged from the ALL in order to open the ALL door so that film can be thrust from the film cartridge. The loading force required to disengage the lock pawl from the ALL is the largest of all the loading forces which must be provided to the film cartridge during loading of the cartridge into the loading chamber. Other lesser loading forces must also be applied to the cartridge during loading.
One method for loading a film cartridge into a camera provides for a single loading force which is larger than the largest force experienced by the film cartridge during loading. As described in the camera system above, the lock pawl disengagement force is the largest resistance that must be overcome during cartridge loading. In this loading method, the camera user pushes the film cartridge partially into the camera loading chamber and then closes a film door. The user then pushes the film door towards a closed position causing the door to engage the cartridge to push the film cartridge the rest of the way into the camera chamber.
Using this loading method, camera film doors are typically designed to withstand the maximum force required to load a film cartridge into a camera when the film door is closed. This results in film doors that have large spring mechanisms for closing the door, and significantly thick cross-sections. Such film doors, are harder for the user to close, weigh more than is desired and have larger space requirements than is desired for use in small, light weight cameras. It is therefore desired to have a film door that is light weight, has a minimum volume and requires a minimum spring force to properly locate a film cartridge.
U.S. Pat. No. 5,255,034 discloses a camera in which a guide member support shaft is fixed to a cover in an internal central portion of the cover. A guide member is provided rotatably around the support shaft and is actuated downward by a spring to engage with a not-projecting cylindrical patrone shaft. The guide member regulates the position of the film patrone in an axial direction. The surface of the guide member engaging with the patrone shaft is a conical surface which causes the film patrone to be eccentric with respect to the patrone chamber by means of the spring. Such disclosure does not provide any feature on the cover for pushing the patrone into the chamber to overcome resistance forces to patrone loading prior to the guide member engaging the patrone shaft. As such, the spring will have to provide a much higher loading force than is necessary to load the patrone into the chamber.